Deal-making in 2017 is off to a rough start, and according to one top dealmaker, the second half of the year is only looking worse.
Despite a few splashy deals such as Amazon and Whole Foods, global mergers and acquisition (M&A) volume for the first half of the year hit $1.59 trillion dollars—which was about 4 percent shy of 2016's half-year total of $1.66 trillion.
When singling out U.S.-targeted deals, the numbers look much more ominous, warned Citigroup's veteran banker.
"[Historically], the second half is 20 percent better than the first half, but even if we get that, we're looking at an M&A market that will be down 10 percent year-over-year in volumes," Citigroup's co-head of Global M&A Mark Shafir told Squawk on the Street Friday.
"So that question is, are we at the beginning of a secular downturn in M&A?"